Variable directivity aerial of the slotted waveguide type



March 17, 1970 M. J. CRUMPEN 3,501,766

VARIABLE DIRECTIVITY AERIAL OF THE SLOTTED WAVEGUIDE TYPE Filed July 2'7, 1966 FIG.

BY A A-r ro 2:490

3,501,766 VARIABLE DIREC- IYITY AERIAL OF THE SLOTTED WAVEGUIDE TYPE James Crumpen, Essex, England, assignor to Mervyn London, England, a

The Marconi Company Limited, British company Filed July 27, 1 966, Ser. No. 568,163

Claims priority, application Great Britain, Aug. 16, 1965,

Int. CI. 11016;" 13/10, 15/02, 1/42 US. Cl. 343771 Claims ABSTRACT OF THE DISCLOSURE This invention relates to variable directivity aerials that is to say to directional aerials in which the directionof maximum signal strength can be varied or swung over a small arc. More specifically the invention relates to variable directivity aerials of the slotted waveguide type.

The slotted waveguide type of directional aerial is well known. In its usual form it consists of a length of rectangularly sectional waveguide with an array 'of slots in one of its narrow walls. It is often required to vary the direction of maximum signal strength ofsuch an aerial so as to swing the main polar radiation lobe over a small arce.g. an arc of 2". This requirement can be satisfied by varying the frequency but this is frequently inconvenient and sometimes not permissible. One known way of securing the required variation of directivity without changing the frequency is to construct the guide with one narrow wall opposite the slotted narrow wall mechanically separate from the other three walls and to mount this mechanically separate wall so that it can be moved towards or away from the slotted wall over a small distance, thus varying the separation of the two narrow walls to vary the directivity. This expedient, however, involves the use of a construction which is expensive and difiicult to manufacture so as to be satisfactory and of accurately predictable constant performance.

The present invention seeks to provideimproved variable directivity aerial systems of the slotted waveguide type wherein the directivity can be varied without changing the operating frequency and without changing the geometry of the waveguide itself. The invention thus enables slotted waveguides of normal predetermined and fixed construction to be used. 4

According to this invention a variable directivity aerial system comprises a slotted waveguide aerial and, in combination therewith, an additional member which is movably mounted near the slots of the guide and is adapted differently to modify the field in the neighbourhood of the slots in different positions occupied by said'member in its range of movement.

The additional member may be a metal member which is movable through a range of positions in all of which it does not obstruct the main polar radiation lo'be. For example the additional member maybe a metallic sheet which is pivotally mounted about an axis which is parallel to the axis of the guide but lies outside the section of said guide, said sheet having a portion which projects 3, 15,76 Fatented Mar. 17, 1970 beyond the slotted wall of said guide and being movable into positions in each of which it lies in a plane at a different angle to a broad wall of the guide. In another embodiment the additional member is a metallic sheet which is situated outside the section of the guide and has a portion projecting beyond the slotted wall of the guide, said sheet being so mounted as to be movable to occupy positions in different parallelplanes at different distances from a broad wall of the guide. 5 v

The additional member may, however, be of thin microwave permeable insulating material-4m example siliconloaded fibre-glass about A of an inch thick Such material is nearly, though not quite, transparent, to microwaves offering some obstruction to the passage of microwaves therethrough. An additional member for example in the form of a sheet made of such material may be employed if arranged in -front of the slotted wall of the guide adjacent the slots thereof and movable in respect 'ther eto so as to vary its distance from said slots. The

insulating additional member may be pivotally mounted about an axis which is parallel to the guide axis or it may be movable to occupy positions in different parallel planes at different distances from the slotted wall of the guide. Where the additional member is of insulating material it may form part of an insulating housing or so-called radome for the slotted guide and the whole housing or radome may be movable. to provide the required movement of the part thereof constituting the said additional member.

The invention is illustrated in the accompanying drawings which show purely schematically four embodiments thereof.

In the drawings:

FIGURE 1 is a diagrammatic perspective.v view of one embodiment of the invention in which a sheet, in addition to the slotted aerial structure,'is pivotally mounted about I an axis which is parallel to the axis of the guide and lies outside the section of the guide;

FIGURE 2 is a view similarto FIGURE 1 of a modified embodiment in which the additional sheet is movable to positions in different parallel planes at different dis tances from a broad wall of the guide; 1

FIGURE 3 is a diagrammatic perspective viewof another modified embodiment in which the additional sheet is positioned in front of the slotted wall of the guide adjacent to the slots thereof and is movable towards and away from the slotted Wall; and, FIGURE 4 is a view similar to FIGURE 3 but showing a further modification in which the additional sheet is mounted to pivot about an axis parallel to the guide axis.

Referring to FIGURE 1 aerial system therein illustrated includes a rectangulai'ly sectioned length of multiwalled waveguide 1 having an array of slots 2 in one conventionally indicated. Under one broad wall of the guide there is provided, in accordance with this invention,

a metal sheet member 3. This member is pivotally mounted about an axis 4 which is parallel to the guide axis and is shown positioned near the guide edge where the lower broad wall meets the unslotted narrow wall. In the position .in which member 3 is shown in FIGURE 1 it is parallel to the broad wall but can be swung up or down out of parallelism as indicated by the double headed curved arrow. The edge of the member 3 remote from the pivotal axis projects beyond the slotted wall of the guide. Dimensions are not critical 'but a projection of about 0.1x (where A is the intended working wavelength) is a practical figure and a spacing of the member 1 below the lower broad wall of the guide (when said member and wall are in parallel planes) of about 0.2). is also a practical figt ire. With these spacings employed in an embodiment designed for operation at about 8800 mc./ s. and the pivotal axis lying parallel to the guide axis in the plane containing the unslotted narrow wall, it was found possible to swing the member 3 towards the guide through an angle ofabout 15 from the position in which it was parallel to the adjacent broad wall of the guide and swinging of the member 3 through :15 from said parallel position was efiective to swing the maximum polar radiation lobe through about 1-1" from a position in which it was inclined at about 67 to the plane of the slotted wall.

The modification shown in FIGURE 2 differs from that of FIGURE 1 only in that the member 3, instead of being pivoted, is movable up and down to occupy positions in planes which are parallel to one another and to those of the broad walls of the guide. The arrows in FIGURE 2- indicate this movement provision.

In FIGURES 3 and 4 the movable member is a sheet of micro-wave permeable insulating material. Siliconloaded fibre-glass 92 thousandths of an inch thick has been found 'satisfactory. In these figures the sheet is referenced 33 and is positioned in front of the slotted guide wall. In FIGURE 3 it is movable to occupy positions in planes which are parallel to one another and to those of the narrow walls of the guide. To quote practical figures a movement of about '-0.25" about a mean position in which the spacings of member 3 is about 0.375 from the slotted guide wall will give results similar to those already described with reference to FIG- URE 1, i.e. a polar radiation lobe swing of about :1".

FIGURE 4 differs from FIGURE 3 in that the sheet 33 is pivoted so as to oscillate about an axis 44 as indicated by the double headed curved arrow.

The members 3 and 33 are shown in the figures as planar. This is not, of course, a necessary feature and curved shapes may be used. In FIGURES 3 and 4 and in other embodiments employing insulating members 33, the said member may form part of a weather protecting so-called radome which may be movable as a whole to impart the required adjustment or variation of the position of the member which forms part of it.

In all the embodiments variation of directivity is obtained as a result of modification of the field in the neighbourhood of the slots.

I claim:

I. A variable directivity aerial system comprising a l multi-walled waveguide aerial, the walls of which are in fixed relation to one another and one of said walls having an array of a plurality of slots, and, in combination therewith, an additional member which is movably mounted near the slots of said one of said walls, said additional member being of thin micro-wave permeable insulating material offering some obstruction to the passage of micro-waves therethrough and being adapted differently to modify the field in the neighborhood of the slots indifferent positions occupied by said member in its range of movement, wherpby by changing the position of said member relativeto said slots the direction of maximum signal strength may be swung over a small are by varying the field in the region of said slots without changing frequency or moving said waveguide serial.

2. A system as claimed in claim 1 wherein the additional member is in the form of a movable sheet arranged in front of the slotted wall of the guide adjacent the slots thereof and movable in respect thereto so as to vary its distance from said slots.

3. A system as claimed in claim 2 wherein the sheet is pivotally mounted about an axis which is parallel to the guide axis.

4. A system as claimed in claim 2 wherein the sheet is movable to occupy positions in different parallel planes at different distances from the slotted wall of the guide.

5. A system as claimed in claim 1 wherein the additional member forms part of an insulating radome housing for the slotted guide and the Whole housing which is movable as a whole to provide the required movement of said members.

References Cited UNITED STATES PATENTS 2,452,349 10/1948 Becker 34376l XR 2,934,762 4/1960 Smedes 343756 XR 2,764,756 9/1956 Zaleski 343-756 XR 3,044,067 7/1962 Butson 343839 XR 2,996,715 8/1961 Rumsey et al. 343786 XR 3,018,479 1/1962 Kelly 343768 XR 3,377,596 4/1968 Spitz 343768 HERMAN KARL SAALBACH, Primary Examiner 0 MARVIN NUSSBAUM, Assistant Examiner US. Cl. X.R. 343--872, 909 

